auctex - What is the difference of tex-mode and latex-mode and LaTeX-mode in emacs -

i configuring auctex in emacs.

most of configurations put in latex-mode-hook. when open main.tex file, notice major mode latex-mode , hooked configurations not activated. have m-x tex-latex-mode activate them. major-mode still latex-mode.

(add-hook 'latex-mode-hook       (lambda ()          ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;         ;; auctex          (setq tex-auto-save t)         (setq tex-parse-self t)        )) 

so know difference of these modes , how can turn on auctex automatically when open *.tex file.

the modes provided auctex listed @ https://www.gnu.org/software/auctex/manual/auctex.html#modes-and-hooks , are

• plain-tex-mode
• latex-mode
• ams-tex-mode
• context-mode
• texinfo-mode
• doctex-mode

instead,

• tex-mode
• plain-tex-mode
• latex-mode
• slitex-mode
• doctex-mode

(note different capitalization) major modes provided tex mode package shipped emacs.

if want open *.tex files auctex latex mode add .emacs:

(add-to-list 'auto-mode-alist '("\\.tex$" . latex-mode)) 

actually, shouldn't necessary, because auctex defines tex-mode.el mode names alias of own modes.